1. Field of the Invention
The present invention relates to a framing bar connecting method for forming a frame by assembling framing bars of a light metal, such as aluminum.
2. Description of the Prior Art
To form such a frame by assembling framing bars, an L-shaped connecting plate having right-angled arms which are inserted in dovetail grooves formed in the adjacent framing bars, respectively, has been used. There are various fixing means for fixing the connecting plate to the framing bars. For example, the arms of a connecting plate are wedged into the dovetail grooves of the adjacent framing bars, the serrated arms of a connecting plate are driven into the dovetail grooves of the adjacent framing bars so that the serrations cut into the inner surfaces of the dovetail grooves or the arms of a connecting plate are inserted in the dovetail grooves of the adjacent framing bars and are fastened to the framing bars with screws.
Most conventional connecting plates need to be struck to drive the arms into the dovetail grooves of the adjacent framing bars. Therefore, it is possible that the framing bars are damaged or warped by the impact applied to the connecting plate, and the joint is liable to become loose or the adjacent framing bars are dislocated relative to each other. Fastening the connecting plate to the framing bars with screws requires much time and reduces the efficiency of frame assembling work.
To overcome such disadvantages of the conventional connecting plate, various framing bar connecting methods applying the principle of a lever have been proposed and applied practically. These framing bar connecting methods do not require striking the connecting member and enable fixedly connecting the framing bars through simple operation. Typically, those framing bar connecting methods employ a lever provided with an eccentric cam at the base end thereof and, in fastening a connecting plate to the framing bar, the lever is turned so that the eccentric cam urges the connecting plate away from the bottom surface of the dovetail groove of the framing member and presses the connecting plate against the inner surfaces of the upper edges of the dovetail groove.
Ordinarily, such a lever is formed by casting a hard metal such as iron because the lever has a complex shape, while the framing bar is formed of a soft light metal such as aluminum. Accordingly, the nose of the eccentric cam bites deep in the bottom surface of the dovetail groove of the framing bar to make turning the lever difficult and, in the worst case, the pivots extending across the eccentric cam is broken when the lever is turned forcibly. Since the bottom surface of the dovetail groove is thus scraped and damaged by the eccentric cam, the fastening force of the lever is not applied effectively to the connecting plate and the framing bar and, when the frame is assembled and disassembled repeatedly, the fastening effect of the lever is reduced accordingly.